Graphite Composite Particle Morphology Control for Battery Capacity
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Solution Overview
Problem
Nonaqueous secondary batteries face challenges in achieving high capacity with a small charge-discharge irreversible capacity, particularly when increasing the density of the active material layer on the negative electrode, as existing methods like Patent Document 1 fail to adequately reduce irreversible capacity while maintaining high capacity.
Innovation Solution
The use of graphite composite particles with specific properties, including a controlled ratio of median size and Raman R value, connected by a graphitizable binder, which are used to form a negative electrode active material that reduces irreversible capacity while maintaining high capacity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the density of the active material layer is increased to obtain high capacity, then the battery capacity is improved, but the charge-discharge irreversible capacity at initial cycle increases
Solution Approach 1:
The invention changes the particle size parameters of the graphite composite particles, specifically controlling the ratio of volume-based median particle size to average circle-equivalent particle size to be 1.05 to 1.30, and controlling the Raman R value to be 0.11 to 0.15. These parameter changes optimize the particle morphology to reduce irreversible capacity while maintaining high capacity even at increased active material layer density.
Solution Approach 2:
The invention uses composite graphite particles formed by carbonizing a binder around a core material, creating a composite structure that combines the high capacity of graphite with the beneficial effects of the carbonized binder shell. This composite structure reduces irreversible capacity while maintaining high capacity.
2Quantity of substance
If the density of the active material layer is increased to obtain high capacity, then the energy density is improved, but the initial cycle efficiency deteriorates
Solution Approach 1:
The invention optimizes particle size parameters (volume-based median particle size to average circle-equivalent particle size ratio of 1.05 to 1.30) and Raman R value (0.11 to 0.15) to achieve better initial cycle efficiency while maintaining high energy density through increased active material layer density.
Solution Approach 2:
The carbonized binder forms a protective shell around the core material during particle formation, creating a stable surface structure before electrode assembly. This preliminary structural preparation reduces initial cycle irreversible capacity while enabling high energy density.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach enables the production of nonaqueous secondary batteries with high capacity and a small charge-discharge irreversible capacity at the initial cycle, even when the active material layer density is increased, thereby improving battery performance and efficiency.
Implementation Method 1
the binder is carbonized by primary heating at 700 to 1,500°C
Implementation Method 2
a purification of the natural graphite and a graphitization of the carbonized binder are simultaneously performed
Implementation Method 3
a Raman R value, which is an intensity ratio of a maximum peak at 1,580 cm-1 and a maximum peak at 1,350 cm-1 in a Raman spectrum of the graphite composite particle, is 0.11 to 0.15
Data Source
AI summary
To provide a nonaqueous secondary battery ensuring that a charge-discharge irreversible capacity at an initial cycle is sufficiently small even when an active material layer comprising a negative electrode active material on a current collector is increased in a density for obtaining a high capacity. This object is attained by a graphite composite particle for a nonaqueous secondary battery, which satisfies the requirements (1) and (2): (1) DL/DS is more than 1 and 2 or less, wherein DL µm means a volume-based median size measured by a laser diffraction/scattering-type particle size distribution measuring apparatus, and Ds µm means an average circle-equivalent particle size which is determined from a measured area S of particles each having a contour not overlapped with a contour of another particle in a SEM; and (2) a Raman R value is 0.04 or more and 0.14 or less, wherein the Raman R value means an intensity ratio IB/IA between an intensity IA of a maximum peak of 1580 cm-1 around and an intensity IB of a maximum peak of 1360 cm-1 around in a Raman spectrum.